The present invention relates to genetically engineering banana plants and, more particularly, to introducing exogenous disease resistance traits to banana plants.
The global banana production exceeds 80 million tones annually and serves as an essential food item to about 400 million people residing in tropical and subtropical developing countries. In addition, banana produce is exported at a gross value exceeding 3 billion US$ annually thus providing a most necessary income of foreign currency to many developing countries.
The banana production is presently threatened by devastating diseases caused by pathogenic fungi, particularly the black leaf streak disease (BLSD) caused by Mycosphaerella fijiensis Morelet and the Sigatoka disease (SD) caused by M. musicola Leach ex Mulder. These pathogens attack all types of banana and are widespread in most banana producing regions where yield losses due to BLSD and SD may reach up to 30-50%.
Banana diseases caused by pathogenic fungi, such as BLSD and SD may be treated by fungicides, however effective fungicides are often too costly for use in developed countries. Furthermore, the presence of fungicide residue in exported fruit is increasingly restricted, due to health and environmental concerns, thus further limiting the practice of chemical control. Banana disease control by way of sanitation has been proven ineffective since it requires disciplined use of pathogen-free germplasm which is often lacking among growers in developing countries and since pathogens are capable of spreading via wind-borne spores.
A preferred approach for effectively controlling banana diseases, such as BLSD and SD, is by generating disease resistant banana cultivars. Traditional breeding of banana plants has produced BLSD-resistant diploid banana cultivars [e.g., “Paka” (AA) and “Pisang lilin” (AA)] however, disease-resistant triploid cultivars, such as “Cavendish” type dessert banana, have not been developed (Mourichon et al. 1997). Since traditional breeding of banana is hampered by long generation time (almost two years), large areas for field testing (6 m2 per plant), triploidy and sterility of most edible cultivars, the use of genetic engineering techniques for conferring disease resistance to banana plants is highly desired (Sagi et al., 1995).
One approach of transforming banana plants involves the use of Agrobacterium-mediated delivery of exogenous DNA. For example, U.S. Pat. No. 6,133,035 describes a method of transforming banana through incubation with Agrobacterium cells carrying exogenous DNA including selectable marker genes nptII or ALS and a GUS reporter gene.
Another approach of transforming banana plants involves bombardment of embryogenic cells with accelerated micro-particles carrying exogenous polynucleotides (microprojectiles). For example, Dugdale et al. (Journal of General Virology 79:2301-2311, 1998) describe transformation of embryogenic suspended cells of banana cv. “Bluggoe” (Musa, ABB group) by using microprojectiles bombardment. The microprojectiles used in transformation carried exogenous DNA including selectable marker genes, reporter genes (e.g., GUS or green fluorescent protein encoding sequence) and the banana bushy top virus DNA-6 promoter. The reporter genes were stably integrated in banana cells genomes and expressed in plants regenerated therefrom.
Yet, the prior art fails to describe successful generation of banana plants having disease resistance traits.
While reducing the present invention to practice, the present inventors successfully produced banana plants which carry and express exogenous polynucleotides encoding disease resistance traits.